Liquid aeration delivery apparatus

ABSTRACT

The invention is to prevent a nozzle located at a position immediately preceding a mixing chamber from becoming closed off with crystallized solute contained in a liquid which has become deposited and to prevent air supplied into the mixing chamber from flowing backward to a metering pump in a liquid aeration delivery apparatus for mixing the liquid with the air and delivering it. Accordingly, a liquid pressurized at a metering pump is supplied via an outlet flow passage and is injected into a mixing chamber from an orifice, but a needle is inserted into the orifice and is made to move by an electromagnetic valve used to open/close the outlet flow passage, so that the orifice is cleaned. In addition, air for mixture is supplied to the mixing chamber, but a pulse synchronous with a pulse applied to the metering pump is supplied to an air control valve provided at an air flow passage, so that supply of the air can be synchronized with the liquid supply to prevent an air backward flow. This invention is also to prevent the liquid from freezing and to prevent the internal pressure from rising to an abnormally high level.

BACKGROUND OF THE INVENTION

The present invention relates to a liquid aeration delivery apparatus inwhich a liquid such as urea water used for purposes of exhaust gaspurification is mixed with air and then delivered.

Urea water (a urea aqueous solution) is widely used as a reducing agentin the purification of exhaust gas from diesel engines and the like. Asdisclosed in JP H7-279650 A, JP 2000-8833 A, JP 2003-232215 A and U.S.Pat. No. 3874822, for instance, urea water is injected through aninjection nozzle into a discharge pipe located further toward theexhaust gas upstream side relative to the reduction catalyst. Theinjected urea water becomes hydrolyzed with the heat from the exhaustgas, thereby generating ammonia, and NO_(x) in the exhaust gas isreduced by the ammonia thus generated on the catalyst. Namely, theNO_(x) is converted to harmless substances, i.e., nitrogen (N₂) andwater (H₂O).

The urea water used as the reducing agent in the process described aboveis supplied by a pump, is mixed with air in a mixing chamber locatedhalfway through the supply path and reaches the nozzle through which itis injected into the discharge pipe in an aerated and atomized state.

Urea water used in the application described above has a disadvantage inthat an orifice located at a position immediately preceding the mixingchamber becomes closed off by urea which has become deposited from thesolution and has become crystallized during an operation us well as whenthe pump is in a stopped state. In addition, if an electromagnetic pumpwhich is caused to make reciprocal movement by a pulse current isutilized as the pump, the supply pressure with which the urea water isoutput pulsates synchronously with the number of pulses. This is thenatural outcome of the pulse-driven electromagnetic pump making thereciprocal movement. The pulsating supply pressure may become lower thanthe pressure of the air supplied into the mixing chamber to be mixedwith the urea water, and in such a case, the air is allowed to flow inthe reverse direction toward the pump, if only temporarily, whichaffects the injection quantity at the nozzle to lead to destabilizationof the injection quantity. This gives rise to a problem such that thestability and reproducibility of the injection quantity are compromised.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to prevent the nozzlefrom becoming clogged even when a solute of the solution becomesdeposited and to prevent the air which is mixed with the liquid in themixing chamber from flowing backward to the metering pump that suppliesthe liquid.

Other objects of the present invention are to prevent the liquid fromfreezing and to prevent the internal pressure from rising to anabnormally high level.

A liquid aeration delivery apparatus according to the present inventioncomprises at least a metering pump which can control an output volume;an outlet flow passage provided on an outlet side of said metering pump;a mixing chamber provided at an end of said outlet flow passage, inwhich a liquid supplied from the metering pump is mixed with air; anorifice through which the liquid is supplied into the mixing chamber; anelectromagnetic valve for opening/closing the out flow passage; and aneedle inserted at the office and moving in cooperation withopening/closing movement of the electromagnetic valve.

Since the orifice is constantly cleaned by moving the needle with theelectromagnetic valve for opening/closing the outlet flow passage, thesubstance contained in the liquid (urea water) force-fed from themetering pump, which has become deposited and crystallized, is notallowed to clog the orifice.

The liquid aeration delivery apparatus further comprises a means forpreventing backward flow which prevents backward flow of air from themixing chamber to the metering pump.

In the structure described above, the orifice is constantly cleaned bymoving the needle via the electromagnetic valve for opening/closing theoutlet passage to prevent a substance contained the liquid, havingbecome deposited and crystallized, from clogging the orifice. Inaddition, since it has the means for preventing backward flow, thebackward flow from of air from the mixing chamber is prevented, so thatinjection quantity can be stabilized.

The means for preventing backward flow is an air control valve which isprovided in an air flow passage for supplying air to said mixingchamber; said air control valve closing said air flow passage innon-operating state, a drive pulse of said metering pump applying tosaid air control valve in operating state to be driven synchronouslywith said metering pump.

Accordingly, the air control valve can be controlled synchronously witha drive pulse of the metering pump, so that air's discharge to themixing chamber can be stopped synchronously to prevent the air backwardflow.

It is preferred that the means for preventing backward flow is to makesaid electromagnetic valve opening/closing movement synchronously with adrive pulse of said metering pump. Accordingly, the outlet flow passageis closed synchronously by operating the electromagnetic valvesynchronously with the drive pulse of the metering pump to prevent theair backward flow.

The metering pump includes an electromagnetic coil to which a pulsecurrent is applied, a plunger which is caused to move reciprocally bythe electromagnetic coil, and an intake valve and an outlet valve thatin conjunction with the plunger, achieve a pump function. The meteringpump also includes a stopper that comes into contact with the plungerpressed by a resilient spring provided at one side of the plunger and amagnetic pole which attracts the plunger toward the spring at theplunger. As a result, an advantage is achieved in that the plunger isallowed to start moving away from the stopper any time by applying apulse, which in turn, allows the metering pump to vary its output volumeover a wide application frequency range.

A pressure sensor that also functions as an accumulator may be providedat the outlet flow passage extending from the metering pump and themixing chamber so as to use the output of the pressure sensor as anindicator to monitor the operation of the aeration atomizing apparatus.In this case, the operating state can be ascertained based upon theoutput of the pressure sensor. In addition, at the pressure sensor, thepressure inside the outlet flow passage is received via a diaphragm, apiston having a magnet is disposed on the side of the diaphragm oppositefrom the side where the pressure is received and any displacement of thepiston is detected with a magnetic sensor.

A temperature sensor may be provided within the outlet flow passageextending from the metering pump to the mixing chamber or in thevicinity of the outlet flow passage. By adopting this structure, itbecomes possible to detect freezing of the urea water inside the pumpcaused by a decrease in the outside air temperature or any abnormal heatgeneration.

A liquid aeration delivery apparatus according to the present inventionfurther comprises a means such that heat is generated by applying a DCcurrent to the electromagnetic coil if the temperature sensor detects atemperature level equal to or lower than a predetermined level in anon-operating state thereof and the current applied to theelectromagnetic coil is turned on/off based upon the output from thetemperature sensor. Accordingly, the temperature of the liquid insidethe pump is monitored by the temperature sensor, and the DC current issupplied to the electromagnetic coil at the metering pump if the liquidtemperature is lowered to the freezing level to generate heat and thusprevent freezing. It is to be noted that the power is turned on as theliquid temperature becomes lower than −7° C. and is turned off once theliquid temperature reaches 0C.

Furthermore, a liquid aeration delivery apparatus according to thepresent invention further comprises a means for preventing an innerpressure from rising to an excessively high level such that theelectromagnetic valve controlling opening/closing of the outlet flowpassage is opened if the pressure sensor detects that the pressure inthe metering pump and in the outlet flow passage has risen to a levelequal to or higher than a predetermined level in an non-operating statethereof Since it is possible to release the pressure to the outside byopening the electromagnetic valve when, for instance, the volume of theliquid in the pump has increased due to freezing by adopting thisstructure, the pump does not become ruptured. It is to be noted thatwhen the liquid temperature is lowered to the freezing level, thetemperature sensor described earlier also functions in conjunction withthe pressure sensor to keep the pressure from rising.

As described above, according to the present invention, the displacementof the electromagnetic valve for opening/closing the outlet flow passagecauses the needle to move to constantly clean the orifice and, as aresult, a substance contained in the liquid (e.g. urea water) beingforce-fed, having become deposited and crystallized, does not clog theorifice.

Furthermore, the means for preventing backward flow for preventing airbackward flow from the mixing chamber stops supplying air or closes theoutlet passage even if an output pressure of the liquid from themetering pump is in a low level, so that the backward flow can beprevented. Accordingly, stabilization of the injection quantity isachieved.

The air supplied for mixing is supplied into the mixing chambersynchronously with the drive pulse of the metering pump by the aircontrol valve, so that the backward flow can be prevented.

Also, since the electromagnetic valve closes the outlet passagesynchronously with an output pulsation of the liquid from the meteringpump when an output pressure of the liquid from the metering pump is ina low level, the air backward flow is prevented to achieve stabilizationof injection quantity. Accordingly, in this case, the air control valvecan be omitted to distribute to minimization of a device.

The plunger is allowed to start moving away from the stopper any time byapplying a pulse, which in turn, allows the metering pump to vary theoutput volume over a wide application frequency range.

The pressure sensor is utilized as an indicator for operationalmonitoring as well as a pressure gauge. Accordingly, it becomes possibleto infer the proper function of the metering pump.

The pressure sensor disclosed in the invention is a simpler structure.

Temperature management in the apparatus may become possible by thetemperature sensor according to the present invention.

Furthermore, according to the present invention, if the temperaturesensor detects a freezing temperature level in a non-operating state, aDC current is supplied to the electromagnetic coil at the metering pumpto generate heat and the current applied to the electromagnetic coil iscontrolled based upon the temperature detected at by the temperaturesensor.

In addition, according to the present invention, a rupture is preventedby opening the electromagnetic valve for opening/closing the outlet flowpassage and thus releasing the pressure to the outside if the pressuresensor detects that the pressure has risen to a dangerously high levelin a non-operating state.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a liquid aeration delivery apparatusaccording to a first embodiment of the present invention;

FIG. 2 is a sectional view of the metering pump which is a component ofthe liquid aeration delivery apparatus according to the firstembodiment;

FIG. 3 is a sectional view of the mixing device which is a component ofthe liquid aeration delivery apparatus according to the firstembodiment;

FIG. 4 is a sectional view of the air control valve which is a componentof the liquid aeration delivery apparatus according to the firstembodiment;

FIG. 5 is a sectional view of the pressure sensor which is a componentof a liquid aeration delivery apparatus according to the firstembodiment;

FIG. 6 is a control characteristic flowchart diagram of the firstembodiment of the present invention;

FIG. 7 is a flowchart presenting an example of control implemented toprevent freezing based upon the output from the temperature sensoraccording to the first embodiment of the present invention;

FIG. 8 is a sectional view of a liquid aeration delivery apparatusaccording to a second embodiment of the present invention;

FIG. 9 is a sectional view of the metering pump which is a component ofthe liquid aeration delivery apparatus according to the secondembodiment;

FIG. 10 is a sectional view of the mixing device which is a component ofthe liquid aeration delivery apparatus according to the secondembodiment;

FIG. 11 is a sectional view of the pressure sensor which is a componentof the liquid aeration delivery apparatus according to the secondembodiment;

FIG. 12 is a flowchart presenting an example of control implemented toprevent freezing based upon the output from the temperature sensoraccording to the second embodiment of the present invention; and

FIG. 13 is a control characteristic flowchart diagram of the secondembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a liquid aeration delivery apparatus 1 according to a firstembodiment of the present invention. A metering pump 2 in the liquidaeration delivery apparatus 1 is now explained in reference to FIGS. 1and 2. The metering pump 2 includes a case 4 constituted of a magneticmaterial such as iron and mounted at an apparatus main unit 5 at an openend thereof, and also an electromagnetic coil 6 disposed inside the case4, to which a pulse current is applied from a control unit (not shown).

At the electromagnetic coil 6, which is formed by winding an electricwire around a resin bobbin 3, a non-magnetic guide pipe 9 is fitted at athrough hole 8 passing through the center of the bobbin 3. A right plate10 and a left plate 11 are provided at the right end and the left end ofthe bobbin 3 respectively, to constitute a magnetic circuit togetherwith the case 4.

To the right of the guide pipe 9, a magnetic rod 13 to constitute amagnetic pole is disposed, whereas a stopper 14 is fitted at the leftend of the guide pipe 9. The magnetic rod 13 is constituted of amagnetic material such as iron, with substantially half of the magneticrod 13 on left side inserted at the guide pipe 9 via an O-ring 15 andthe remaining half, i.e., the right half, inserted at a barrel portion19 of an intake coupling 17 to be detailed later via an O-ring 16. Inaddition, a communicating hole 18 passing through along the lateraldirection is formed inside the magnetic rod 13, and the communicatinghole 18 is connected to a urea water tank (not shown). Reference numeral24 indicates a filter provided at the communicating hole 18.

In a communicating hole 20 formed at the magnetic rod 13, a check valve(intake valve) 21 constituted of rubber, resin or the like is disposed,and the check valve 21 made to sit at a valve seat 23 provided at thecommunicating hole 20 with a pressing force imparted by a spring 22.

An electromagnetic plunger operation chamber in which an electromagneticplunger 27 constituted of a magnetic material such as iron is disposedis formed inside the guide pipe 9. The electromagnetic plunger 27includes a large diameter portion 27 a and a small diameter portion 27 bcontinuous to the large diameter portion 27 a and projecting to theright. A through hole 29 is formed along the axial direction at thelarge diameter portion 27 a and the small diameter portion 27 b, and acheck valve (outlet valve) 30 is disposed at the through hole 29 in thesmall diameter portion 27 b and is made to sit at a valve seat 32 with aspring 31. In addition, the small diameter portion 27 b is slidablyinserted at a cylinder 34 mounted at the magnetic rod 13 via an O-ring34 a.

Pressure is applied to the electromagnetic plunger 27 from a returnspring 35 which imparts a strong force and, as a result, although thereis also a spring 37 imparting a force along the opposite direction, theleft end of the electromagnetic plunger 27 is placed in contact with thestopper 14. Namely, if no power is supplied to the electromagnetic coil6, the electromagnetic plunger 27 is set at the return position at whichits left end is in contact with the stopper 14, but whenever a pulse isapplied to the electromagnetic coil 6, the electromagnetic plunger 27 isallowed to start moving away from the stopper 14. It is to be noted thatthe spring 37, which imparts only a weak force, may be omitted dependingupon the particulars of the design requirements.

The left end of the electromagnetic plunger operation chamber 28 is madeto communicate with an outlet flow passage 39 formed at the apparatusmain unit 5 via a hole 38 at the stopper 14, and the outlet flow passage39 extends to a mixing chamber 64 detailed below.

As a pulse current that can be varied over wide range is supplied to theelectromagnetic coil 6 in the metering pump 2 structured as describedabove, the electromagnetic plunger 27 makes reciprocal movement. Namely,as the pulse is supplied, the magnetic rod 13 becomes magnetized and theattraction of the magnetized magnetic rod 13 causes the electromagneticplunger 27 to move against the force imparted by the return spring 35.

Then, as the pulse ceases, the energy stored in the return spring 35resets the left end of the electromagnetic plunger 27 to the position atwhich it comes in contact with the stopper 14. When the pulse is appliedto the electromagnetic coil 6 again, the electromagnetic plunger 27 iscaused to move as described above and thus, a pump function is achievedwith the check valves 21 and 30 through the repeated motion of theelectromagnetic plunger 27. Namely, the liquid, i.e., the urea water, isforce-fed into the mixing chamber 64 with its quantity increasedsubstantially in proportion to the application frequency.

While the metering pump 2 is operated over a wide range with regard tothe pulse applied to the electromagnetic coil 6, the characteristics ofthe electromagnetic pump poses a hindrance to increasing the outputvolume to a desired level simply by increasing the frequency.Accordingly, the metering pump is constituted as a pulse-width dependentconstant-volume electromagnetic pump that varies the pulse width inproportion to the frequency so as to increase the proportion of theoutput volume relative to the proportion of the frequency. The specificranges of frequency between 2 Hz to 40 Hz and pulse width between 5 msand 12.5 ms are selected for illustration in FIG. 6. It is to be notedthat the pulse width and the output volume in the low output volumerange (Min shown in FIG. 6) are respectively 5 (ms) and 1.5(g/min), thepulse width and the output volume in the middle output volume range (Midshown in FIG. 6) are respectively 7.5 (ms) and 30.0 (g/min) and thepulse width and the output volume in the high output volume range (Maxshown in FIG. 6) are respectively 12.5 (ms) and 123.4(g/min). Since “1g” and “1 cc” of pure water are equal in quantity, the unit “g” could bereplaced with “cc” if the liquid was pure water.

Now, a mixing device 43 is explained in reference to FIGS. 1 and 3. Themixing device 43 located on the left side of the apparatus main unit 5includes an electromagnetic valve 44 provided at the left end of theoutlet flow passage 39 to control the open/closed state of the outletflow passage 39. The electromagnetic valve 44 includes a case 45 whichis located on the outside and having an open end thereof attached to theapparatus main unit 5, and also an electromagnetic coil 46 locatedinside the case 45.

At the electromagnetic coil 46, which is formed by winding an electricwire around a resin bobbin 47, a non-magnetic guide pipe 48 is fitted ina through hole passing through the center of the bobbin 47. A rightplate 50 and a left plate 51 are provided at the right end and the leftend respectively of the bobbin 47, to constitute a magnetic circuittogether with the case 45.

A magnetic rod 52 to constitute a magnetic pole is provided to the rightof the guide pipe 48, whereas a valve seat 53 is provided to the left ofthe guide pipe 48. At the magnetic rod 52, constituted of a magneticmaterial such as iron, a communicating hole 54 with an orifice 57 isformed so as to extend along the axis of the magnetic rod 52. Inaddition, an electromagnetic plunger operation chamber 56, in which anelectromagnetic plunger 55 constituted of a magnetic material is housed,is formed inside the guide pipe 48. The electromagnetic plunger 55includes a communicating hole 58 formed so as to extend along thecentral axis, and the electromagnetic plunger 55 is made to sit at thevalve seat 53 by the force applied by a spring 59 to close the outletflow passage 39. Then, as power is supplied to the electromagnetic coil46, the electromagnetic plunger 55 becomes displaced against the forceapplied by the spring 59, thereby opening the outlet flow passage 39. AnO-ring 60 is mounted at the front end of the electromagnetic plunger 55located on the side opposite from the side where the magnetic rod ispresent with a needle 61 projecting out at the same end. The needle 61is inserted at an orifice 62 at the valve seat 53.

The orifice 62 through which the flow rate of the liquid supplied(injected) into the mixing chamber 64 is raised is formed at the centerof the valve seat 53 located at the left end of the guide pipe 48. Asdescribed above, the needle 61 is inserted at the orifice 62 so that asthe electromagnetic valve 44 is turned on/off, the needle 61 becomesdisplaced to clean the inside of the orifice 62.

The mixing chamber 64 is formed inside a connection member 66 having anoutlet port 65, with the orifice 62 described above and an air supplyhole 68 formed at the right end thereof. Thus, air is supplied into themixing chamber 64 in the required quantity from an air tank or the like(not shown) via an air control valve 72 to be detailed below, and theurea water having been injected into the mixing chamber 64 becomesaerated with the air and atomized. Since the air supply hole 68 isconnected to the inner circumferential surface of the mixing chamber 64along the tangential direction, the air is supplied into the mixingchamber 64 in a rotary motion to further promote the aerated atomizationof the urea water. The urea water having been aerated and atomized issent out from the outlet port 65 via a nozzle 69 into a discharge pipewhich is an external device.

The air control valve 72 is now explained in reference to FIGS. 1 and 4.The air control valve 72 located above the apparatus main unit 5includes a case 73 constituted of a magnetic material, provided on theoutside and having an open end thereof mounted at the apparatus mainunit 5, and also includes an electromagnetic coil 74 provided inside thecase 73. At the electromagnetic coil 74, which is formed by winding anelectric wire around a resin bobbin 75, a non-magnetic guide pipe 76 isfitted in a through hole passing through the center of the bobbin 75. Anupper plate 77 and a lower plate 78 are provided at the upper end andthe lower end of the bobbin 75 respectively, to constitute a magneticcircuit together with the case 73.

At the top of the guide pipe 76, a magnetic rod 80 to constitute amagnetic pole is provided, whereas toward the bottom of the guide pipe76, a valve seat 81 is provided. The magnetic rod 80 constituted of amagnetic material such as iron includes a communicating hole 82extending along its axis. Above the magnetic rod 80, an intake coupling85 connecting with an air flow passage 83 through which the air issupplied from the air tank provided. The valve seat 81 includes acommunicating hole 84 which communicates with the mixing chamber 64 onits downstream side via the airflow passage 83. Inside the guide pipe 76partitioned into spaces housing the magnetic rod 80 and the valve seat81 as described above, an electromagnetic plunger operation chamber 87in which an electromagnetic plunger 86 is disposed, is formed.

The electromagnetic plunger 86 includes a communicating hole 89extending along the central axis, and also has a spherical valve element90 mounted at one end thereof. The valve element 90 at theelectromagnetic plunger 86 supported by a pair of springs 91 and 92 andprovided in the electromagnetic plunger operation chamber 87 is made tosit at the valve seat 81 and thus, the communicating hole 84 is closedwhen no power is supplied. Then, as power is supplied, the valve element90 departs from the valve seat 81 to open the communicating hole 84.

The air control valve 72 structured as described above is controlled byapplying a pulse current to the electromagnetic coil 74. The air controlvalve 72 is driven synchronously with the drive pulses of the meteringpump 2 when a pulse width applied to the metering pump 2 is narrow(namely, a low output volume range Min), as shown in FIG. 6, in relationto the metering pump 2.

Namely, a drive pulse with a rising side synchronous with a falling sideof the drive pulse of the metering pump is made at the low output volumerange (Min) of the metering pump 2. It is preferred that a delayprocessing which delays the up of the drive pulse is operated. A widthof the drive pulse of the air control valve 72 is limited by a risingside of a next drive pulse of the metering pump 2.

Since the air to be mixed with the urea water achieves a constantpressure of 15 psi and thus there is a risk of the air flowing backwardunless the air is supplied synchronously when the injection quantity ofthe urea water injected from the metering pump 2 is small, i.e., in aso-called low pulse rate condition (Min shown in FIG. 6), and thepulsating pressure inherent to the electromagnetic pump dips lower thanthe air pressure. The drive pulse of the air control valve can resolvethe risk.

A pressure sensor 93 is described in reference to FIGS. 1 and 5. Apressure sensor main unit 94 fitted in the apparatus main unit 5 assumesa tubular shape and includes a piston 96 disposed inside a centralchamber 95 and having a magnet 98, with a spring 97 applying a force tothe piston 96. At the center of the piston 96, a magnetic sensor 99,which may be a Hall IC or a magnetic resistor element that reacts tomagnetism, is provided. The magnetic sensor 99 is located at a rod 100screwed onto the pressure sensor main unit 94 and the sensor sensitivityis adjusted by varying the position of the rod 100.

The pressure sensor main unit 94 assuming the structure described aboveis fitted in the apparatus main unit 5 via a diaphragm 101 which isconnected to the outlet flow passage 39 formed at the apparatus mainunit 5 via a branch flow passage 39 a. Thus, as the pressure in theoutlet flow passage 39 increases, the diaphragm 101 becomes displacedand, at the same time, the piston 96, too, becomes displaced against theforce applied by the spring 97. The displacement of the piston 96 isdetected with the magnetic sensor 99, and it becomes possible to inferthe proper function of the metering pump according to displaying thesensor output (an output characteristic of the pressure sensor shown inFIG. 6).

Based upon the output from the pressure sensor 93, any abnormal increasein the pressure in the outlet flow passage 39 can be detected, and ifthe pressure rises to an abnormally high level, power is supplied to theelectromagnetic coil 46 at the electromagnetic valve 44 describedearlier to open the electromagnetic valve 44, thereby releasing thepressure to the outside and, as a result, any rupture is prevented.

Besides, it is not necessary to define the pressure sensor 93 to only astructure for detecting displacement as above-mentioned. It may have astructure which is provided with a means for detecting distortion by thepressure, a means for detecting thermoelectromotive force by thepressure dependence of the thermal conductivity, a means for detecting avoltage by the pressure dependence of the break-down voltage, a meansfor detecting an ionic current due to gaseous ionization phenomenon, ameans which detects a phase due to the interference phenomenon of thelight, or a means for detecting the strength of the light due to microvent loss.

Now, in reference to FIGS. 1 and 7, a temperature sensor 103 isdescribed. The temperature sensor 103 constituted of a thermistorprovided near the outlet flow passage 39 in the apparatus main unit 5detects the temperature of the apparatus. It becomes engaged inoperation as the external air temperature becomes low in a non-operatingstate to prevent the urea water from freezing. Besides, it is notnecessary to define the temperature sensor 103 to the thermistor, but athermo couple, a metal resistance temperature sensor (a resistancebulb), heat sensitive magnetic material such as a heat sensitiveferrite, a bimetal thermostat, an IC temperature sensor, an infrared raydetecting element, a crystal temperature sensor, or a fluorescence typefiber temperature sensor can be used.

Namely, as shown in FIG. 7 presenting its control flow, a temperaturesignal provided by the temperature sensor 103 is taken in during atemperature detection step 201. Then, the operation proceeds to step 202to judge the temperature. In this step, a decision is made as to whetheror not the temperature has become equal to or lower than −7° C., and ifit is decided that the temperature is equal to or lower than −7° C. andthus, there is a risk of the urea water freezing, the operation proceedsto step 203 to apply a DC current (DC 24 V) to the electromagnetic coil6 at the metering pump 2. Thus, the electromagnetic valve generatesheat. Then, proceeding to steps 204 and 205, the electromagnetic valve44 and the air control valve 72 are opened.

After that, the temperature sensor 103 monitors the temperature of theapparatus main unit 5, and once the heat rises above 0° C., theoperation proceeds to steps 206, 207 and 208 to stop applying DC currentto the metering pump 2, for the electromagnetic valve to be closed andfor the air control valve to be closed. The urea water is prevented fromfreezing through this control. It is to be noted that since the internalpressure rises if the urea water starts to freeze, the rise in thepressure is detected with the pressure sensor 93 and once the pressurerises to a level exceeding a predetermined level, the electromagneticvalve 44 is opened to preempt any possible problem in conjunction withthe temperature sensor 103.

In the structure described above, a pulse current (2 to 40 Hz) isapplied to the electromagnetic coil 6 at the metering pump 2 and theelectromagnetic plunger 27 is thus caused to vibrate 2 to 40 times persecond to achieve a pump function. This metering pump 2 achieves alinear output which is in proportion to the pulse rate. The liquidsupplied from the metering pump (i.e., the urea water) travels throughthe outlet flow passage 39 and is injected into the mixing chamber 64via the orifice 62, and in the mixing chamber 64, it becomes mixed withthe air supplied thereto.

The orifice 62, which is cleaned with the needle 61, never becomesclogged since urea having been deposited and crystallized which thenadheres to the orifice 62 is removed through the movement of the needle61 caused by the electromagnetic valve 44 at an operation start. Inaddition, in the low output volume range (Min), since control isimplemented with the air control valve 72 to supply the air insynchronization with the supply of the liquid from the metering pump 2,the air is not allowed to flow back toward the metering pump 2, therebyachieving stable injection through the nozzle.

The first embodiment described above is to use an engine of a largevehicle such as a truck, and it is difficult to use in a small sizevehicle with a small displacement because it is too large. Therefore, asecond embodiment of this invention is to use the electromagnetic valve44 installed in the device as the means for preventing backward flow.Thus, the air control valve 72 can be omitted.

FIGS. 8 though 13 show a liquid aeration delivery apparatus 301according to a second embodiment of the present invention. A meteringpump 302 includes a case 304 constituted of a magnetic material such asiron and mounted at an apparatus main unit 305 at an open end thereof asshown in FIG. 9 too, and also an electromagnetic coil 306 disposedinside the case 304, to which a pulse current is applied from a controlunit (not shown).

At the electromagnetic coil 306, which is formed by winding an electricwire around a resin bobbin 303, a non-magnetic guide pipe 309 is fittedat a through hole 308 passing through the center of the bobbin 303. Aright plate 310 and a left plate 311 are provided at the right end andthe left end of the bobbin 303 respectively, to constitute a magneticcircuit together is with the case 304.

To the right of the guide pipe 309, a magnetic rod 313 to constitute amagnetic pole is disposed, whereas a stopper 314 is fitted at the leftend of the guide pipe 309. The magnetic rod 313 is constituted of amagnetic material such as iron, with substantially half of the magneticrod 313 on left side inserted at the guide pipe 309 via an O-ring 315and the remaining half, i.e., the right half, inserted at a barrelportion 319 of an intake coupling 317 to be detailed later via an O-ring316. In addition, a communicating hole 318 passing through along thelateral direction is formed inside the magnetic rod 313, and thecommunicating hole 318 is connected to a urea water tank (not shown).Reference numeral 324 indicates a filter provided at the communicatinghole 318.

In a communicating hole 320 formed at the magnetic rod 313, a checkvalve (intake valve) 321 constituted of rubber, resin or the like isdisposed, and the check valve 321 made to sit at a valve seat 323provided at the communicating hole 320 with a pressing force imparted bya spring 322.

An electromagnetic plunger operation chamber in which an electromagneticplunger 327 constituted of a magnetic material such as iron is disposedis formed inside the guide pipe 309. The electromagnetic plunger 327includes a large diameter portion 327 a and a small diameter portion 327b continuous to the large diameter portion 327 a and projecting to theright. A through hole 329 is formed along the axial direction at thelarge diameter portion 327 a and the small diameter portion 327 b, and acheck valve (outlet valve) 330 is disposed at the through hole 329 inthe small diameter portion 327 b and is made to sit at a valve seat 332with a spring 331. In addition, the small diameter portion 327 b isslidably inserted at a cylinder 334 mounted at the magnetic rod 313 viaan O-ring 334 a.

Pressure is applied to the electromagnetic plunger 327 from a returnspring 335 which imparts a strong force and, as a result, although thereis also a spring 337 imparting a force along the opposite direction, theleft end of the electromagnetic plunger 327 is placed in contact withthe stopper 314. Namely, if no power is supplied to the electromagneticcoil 306, the electromagnetic plunger 327 is set at the return positionat which its left end is in contact with the stopper 314, but whenever apulse is applied to the electromagnetic coil 306, the electromagneticplunger 327 is allowed to start moving away from the stopper 314. It isto be noted that the spring 337, which imparts only a weak force, may beomitted depending upon the particulars of the design requirements.

The left end of the electromagnetic plunger operation chamber 328 ismade to communicate with an outlet flow passage 339 formed at theapparatus main unit 305 via a hole 338 at the stopper 314, and theoutlet flow passage 339 extends to a mixing chamber 364 detailed below.

As a pulse current that can be varied over a wide range is supplied tothe electromagnetic coil 306 in the metering pump 302 structured asdescribed above, the electromagnetic plunger 327 makes reciprocalmovement. Namely, as the pulse is supplied, the magnetic rod 313 becomesmagnetized and the attraction of the magnetized magnetic rod 313 causesthe electromagnetic plunger 327 to move against the force imparted bythe return spring 335.

Then, as the pulse ceases, the energy stored in the return spring 335resets the left end of the electromagnetic plunger 327 to the positionat which it comes in contact with the stopper 314. When the pulse isapplied to the electromagnetic coil 306 again, the electromagneticplunger 327 is caused to move as described above and thus, a pumpfunction is achieved with the check valves 321 and 330 through therepeated motion of the electromagnetic plunger 327. Namely, the liquid,i.e., the urea water, is force-fed into the mixing chamber 364 with itsquantity increased substantially in proportion to the applicationfrequency.

While the metering pump 302 is operated over a wide range with regard tothe pulse applied to the electromagnetic coil 306, the characteristicsof the electromagnetic pump poses a hindrance to increasing the outputvolume to a desired level simply by increasing the frequency.Accordingly, the metering pump is constituted as a pulse-width dependentconstant-volume electromagnetic pump that varies the pulse width inproportion to the frequency so as to increase the proportion of theoutput volume relative to the proportion of the frequency. The specificranges of frequency between 2 Hz to 40 Hz and pulse width between 5 msand 12.5 ms are selected for illustration in FIG. 13. It is to be notedthat the pulse width and the output volume in the low output volumerange (Min shown in FIG. 13) are respectively 5 (ms) and 1.5(g/min), thepulse width and the output volume in the middle output volume range (Midshown in FIG. 13) are respectively 7.5 (ms) and 30.0 (g/min) and thepulse width and the output volume in the high output volume range (Maxshown in FIG. 13) are respectively 12.5 (ms) and 123.4(g/min). Since “1g” and “1 cc” of pure water are equal in quantity, the unit “g” could bereplaced with “cc” if the liquid was pure water.

Now, a mixing device 343 is explained in reference to FIGS. 8 and 10.The mixing device 343 located on the left side of the apparatus mainunit 305 includes an electromagnetic valve 344 provided at the left endof the outlet flow passage 339 to control the open/closed state of theoutlet flow passage 339. The electromagnetic valve 344 includes a case345 which is located on the outside and having an open end thereofattached to the apparatus main unit 5, and also an electromagnetic coil346 located inside the case 345.

At the electromagnetic coil 346, which is formed by winding an electricwire around a resin bobbin 347, a non-magnetic guide pipe 348 is fittedin a through hole passing through the center of the bobbin 347. A rightplate 350 and a left plate 351 are provided at the right end and theleft end respectively of the bobbin 347, to constitute a magneticcircuit together with the case 345.

A magnetic rod 352 to constitute a magnetic pole is provided to theright of the guide pipe 348, whereas a valve seat 353 is provided to theleft of the guide pipe 348. At the magnetic rod 352, constituted of amagnetic material such as iron, a communicating hole 354 with an orifice357 is formed so as to extend along the axis of the magnetic rod 352. Inaddition, an electromagnetic plunger operation chamber 356, in which anelectromagnetic plunger 355 constituted of a magnetic material ishoused, is formed inside the guide pipe 348. The electromagnetic plunger355 includes a communicating hole 358 formed so as to extend along thecentral axis, and the electromagnetic plunger 355 is made to sit at thevalve seat 353 by the force applied by a spring 359 to close the outletflow passage 339. Then, as power is supplied to the electromagnetic coil346, the electromagnetic plunger 355 becomes displaced against the forceapplied by the spring 359, thereby opening the outlet flow passage 339.An O-ring 360 is mounted at the front end of the electromagnetic plunger355 located on the side opposite from the side where the magnetic rod ispresent with a needle 361 projecting out at the same end. The needle 361is inserted at an orifice 362 at the valve seat 353.

The orifice 362 through which the flow rate of the liquid supplied(injected) into the mixing chamber 364 is raised is formed at the centerof the valve seat 353 located at the left end of the guide pipe 348. Asdescribed above, the needle 361 is inserted at the orifice 362 so thatas the electromagnetic valve 344 is turned on/off, the needle 61 becomesdisplaced to clean the inside of the orifice 362.

The mixing chamber 364 is formed inside a connection member 366 havingan outlet port 365, with the orifice 362 described above and an airsupply hole 368 formed at the right end thereof. Thus, air is suppliedinto the mixing chamber 364 in the required quantity from an air tank orthe like (not shown) via an air control valve 372 to be detailed below,and the urea water having been injected into the mixing chamber 364becomes aerated with the air and atomized. Since the air supply hole 368is connected to the inner circumferential surface of the mixing chamber364 along the tangential direction, the air is supplied into the mixingchamber 364 in a rotary motion to further promote the aeratedatomization of the urea water. The urea water having been aerated andatomized is sent out from the outlet port 365 via a nozzle 369 into adischarge pipe which is an external device.

A pressure sensor 393 is described in reference to FIGS. 8 and 11. Apressure sensor main unit 394 fitted in the apparatus main unit 305assumes a tubular shape and includes a piston 396 disposed inside acentral chamber 395 and having a magnet 398, with a spring 397 applyinga force to the piston 396. At the center of the piston 396, a magneticsensor 399, which may be a Hall IC or a magnetic resistor element thatreacts to magnetism, is provided. The magnetic sensor 399 is located ata rod 400 screwed onto the pressure sensor main unit 394 and the sensorsensitivity is adjusted by varying the position of the rod 400.

The pressure sensor main unit 394 assuming the structure described aboveis fitted in the apparatus main unit 305 via a diaphragm 401 which isconnected to the outlet flow passage 339 formed at the apparatus mainunit 305 via a branch flow passage 339 a. Thus, as the pressure in theoutlet flow passage 339 increases, the diaphragm 401 becomes displacedand, at the same time, the piston 396, too, becomes displaced againstthe force applied by the spring 397. The displacement of the piston 396is detected with the magnetic sensor 399, and it becomes possible toinfer the proper function of the metering pump according to displayingthe sensor output (an output characteristic of the pressure sensor shownin FIG. 13).

Based upon the output from the pressure sensor 393, any abnormalincrease in the pressure in the outlet flow passage 339 can be detected,and if the pressure rises to an abnormally high level, power is suppliedto the electromagnetic coil 346 at the electromagnetic valve 344described earlier to open the electromagnetic valve 344, therebyreleasing the pressure to the outside and, as a result, any rupture isprevented.

Besides, it is not necessary to define the pressure sensor 393 to only astructure for detecting displacement as above-mentioned. It may have astructure which is provided with a means for detecting distortion by thepressure, a means for detecting thermoelectromotive force by thepressure dependence of the thermal conductivity, a means for detecting avoltage by the pressure dependence of the break-down voltage, a meansfor detecting an ionic current due to gaseous ionization phenomenon, ameans which detects a phase due to the interference phenomenon of thelight, or a means for detecting the strength of the light due to microvent loss.

Now, in reference to FIGS. 8 and 12, a temperature sensor 403 isdescribed. The temperature sensor 403 constituted of a thermistorprovided near the outlet flow passage 339 in the apparatus main unit 305detects the temperature of the apparatus. It becomes engaged inoperation as the external air temperature becomes low in a non-operatingstate to prevent the urea water from freezing. Besides, it is notnecessary to define the temperature sensor 403 to the thermistor, but athermo couple, a metal resistance temperature sensor (a resistancebulb), heat sensitive magnetic material such as a heat sensitiveferrite, a bimetal thermostat, an IC temperature sensor, an infrared raydetecting element, a crystal temperature sensor, or a fluorescence typefiber temperature sensor can be used.

Namely, as shown in FIG. 12 presenting its control flow, a temperaturesignal provided by the temperature sensor 403 is taken in during atemperature detection step 501. Then, the operation proceeds to step 502to judge the temperature. In this step, a decision is made as to whetheror not the temperature has become equal to or lower than −7° C., and ifit is decided that the temperature is equal to or lower than −7° C. andthus, there is a risk of the urea water freezing, the operation proceedsto step 503 to apply a DC current (DC 24 V) to the electromagnetic coil306 at the metering pump 302. Thus, the electromagnetic valve generatesheat. Then, proceeding to step 504, the electromagnetic valve 344 isopened.

After that, the temperature sensor 403 monitors the temperature of theapparatus main unit 305, and once the heat rises above 0° C., theoperation proceeds to steps 506 and 507 to stop applying DC current tothe metering pump 2 and for the electromagnetic valve 344 to be closed.The urea water is prevented from freezing through this control. It is tobe noted that since the internal pressure rises if the urea water startsto freeze, the rise in the pressure is detected with the pressure sensor393 and once the pressure rises to a level exceeding a predeterminedlevel, the electromagnetic valve 344 is opened to preempt any possibleproblem in conjunction with the temperature sensor 403.

In the structure described above, a pulse current (2 to 40 Hz) isapplied to the electromagnetic coil 306 at the metering pump 302 and theelectromagnetic plunger 327 is thus caused to vibrate 2 to 40 times persecond to achieve a pump function. This metering pump 302 achieves alinear output which is in proportion to the pulse rate. The liquidsupplied from the metering pump (i.e., the urea water) travels throughthe outlet flow passage 339 and is injected into the mixing chamber 364via the orifice 362, and in the mixing chamber 364, it becomes mixedwith the air supplied thereto.

The orifice 362, which is cleaned with the needle 361, never becomesclogged since urea having been deposited and crystallized which thenadheres to the orifice 362 is removed through the movement of the needle361 caused by the electromagnetic valve 344 at an operation start. Inaddition, the electromagnetic valve 344 is operated synchronously withthe drive pulse of the metering pump 302 in order to prevent the airbackward flow to the metering pump 302 in a range from the middle outputvolume range (Mid) to the low output volume range (Min), as shown inFIG. 13.

Namely, in the middle and the law outlet volume ranges, theelectromagnetic valve 344 is opened by a rising side of the drive pulsesynchronously with a falling side of the drive pulse of the meteringpump 302, and is closed by falling down the drive pulse before the nextdrive pulse of the metering pump 302. As a result, since the liquidflows into the mixing chamber when the outlet pressure from the meteringpump 302 is high and the outlet passage 339 is closed to prevent the airbackward flow when the outlet pressure lowers, the injection quantity ofthe liquid is stabilized. Note that a rising of the drive pulse of theelectromagnetic valve 344 is given about 2 ms delay.

1. A liquid aeration delivery apparatus comprising at least: a meteringpump which can control an output volume; an outlet flow passage providedon an outlet side of said metering pump; a mixing chamber provided at anend of said outlet flow passage, in which a liquid supplied from saidmetering pump is mixed with air; an orifice through which said liquid issupplied into said mixing chamber; an electromagnetic valve foropening/closing said out flow passage; and a needle inserted at saidoffice and moving in cooperation with opening/closing movement of saidelectromagnetic valve.
 2. A liquid aeration delivery apparatus accordingto claim 1 further comprising a means for preventing backward flow whichprevents backward flow of air from said mixing chamber to said meteringpump.
 3. A liquid aeration delivery apparatus according to claim 2,wherein: said means for preventing backward flow is an air control valvewhich is provided in an air flow passage for supplying air to saidmixing chamber; said air control valve closing said air flow passage innon-operating state, a drive pulse of said metering pump applying tosaid air control valve in operating state to be driven synchronouslywith said metering pump.
 4. A liquid aeration delivery apparatusaccording to claim 2, wherein: said means for preventing backward flowis to make said electromagnetic valve opening/closing movementsynchronously with a drive pulse of said metering pump.
 5. A liquidaeration delivery apparatus according to claim 1, wherein: said meteringpump is provided with an electromagnetic coil to which a pulse currentis applied, a plunger which is caused to move reciprocally by saidelectromagnetic coil, and an intake valve and an output valve forachieving a pump function in cooperation with said plunger; and saidmetering pump is further provided with a stopper which comes intocontact with said plunger pressed by a spring provided on one side ofsaid plunger and a magnetic pole attracts said plunger toward saidspring.
 6. A liquid aeration delivery apparatus according to claim 2,wherein: said metering pump is provided with an electromagnetic coil towhich a pulse current is applied, a plunger which is caused to movereciprocally by said electromagnetic coil, and an intake valve and anoutput valve for achieving a pump function in cooperation with saidplunger; and said metering pump is further provided with a stopper whichcomes into contact with said plunger pressed by a spring provided on oneside of said plunger and a magnetic pole attracts said plunger towardsaid spring.
 7. A liquid aeration delivery apparatus according to claim3, wherein: said metering pump is provided with an electromagnetic coilto which a pulse current is applied, a plunger which is caused to movereciprocally by said electromagnetic coil, and an intake valve and anoutput valve for achieving a pump function in cooperation with saidplunger; and said metering pump is further provided with a stopper whichcomes into contact with said plunger pressed by a spring provided on oneside of said plunger and a magnetic pole attracts said plunger towardsaid spring.
 8. A liquid aeration delivery apparatus according to claim4, wherein: said metering pump is provided with an electromagnetic coilto which a pulse current is applied, a plunger which is caused to movereciprocally by said electromagnetic coil, and an intake valve and anoutput valve for achieving a pump function in cooperation with saidplunger; and said metering pump is further provided with a stopper whichcomes into contact with said plunger pressed by a spring provided on oneside of said plunger and a magnetic pole attracts said plunger towardsaid spring.
 9. A liquid aeration delivery apparatus according to claim1, wherein: a pressure sensor that also functions as an accumulator isprovided at said outlet flow passage extending from said metering pumpand said mixing chamber so as to use the output of said pressure sensoras an indicator to monitor the operation of said aeration atomizingapparatus.
 10. A liquid aeration delivery apparatus according to claim2, wherein: a pressure sensor that also functions as an accumulator isprovided at said outlet flow passage extending from said metering pumpand said mixing chamber so as to use the output of said pressure sensoras an indicator to monitor the operation of said aeration atomizingapparatus.
 11. A liquid aeration delivery apparatus according to claim3, wherein: a pressure sensor that also functions as an accumulator isprovided at said outlet flow passage extending from said metering pumpand said mixing chamber so as to use the output of said pressure sensoras an indicator to monitor the operation of said aeration atomizingapparatus.
 12. A liquid aeration delivery apparatus according to claim4, wherein: a pressure sensor that also functions as an accumulator isprovided at said outlet flow passage extending from said metering pumpand said mixing chamber so as to use the output of said pressure sensoras an indicator to monitor the operation of said aeration atomizingapparatus.
 13. A liquid aeration delivery apparatus according to claim9, wherein: a pressure inside said outlet flow passage is received via adiaphragm at said pressure sensor, a piston having a magnet is disposedon the side of said diaphragm opposite from the side where the pressureis received and any displacement of said piston is detected with amagnetic sensor.
 14. A liquid aeration delivery apparatus according toclaim 10, wherein: a pressure inside said outlet flow passage isreceived via a diaphragm at said pressure sensor, a piston having amagnet is disposed on the side of said diaphragm opposite from the sidewhere the pressure is received and any displacement of said piston isdetected with a magnetic sensor.
 15. A liquid aeration deliveryapparatus according to claim 11, wherein: a pressure inside said outletflow passage is received via a diaphragm at said pressure sensor, apiston having a magnet is disposed on the side of said diaphragmopposite from the side where the pressure is received and anydisplacement of said piston is detected with a magnetic sensor.
 16. Aliquid aeration delivery apparatus according to claim 12, wherein: apressure inside said outlet flow passage is received via a diaphragm atsaid pressure sensor, a piston having a magnet is disposed on the sideof said diaphragm opposite from the side where the pressure is receivedand any displacement of said piston is detected with a magnetic sensor.17. A liquid aeration delivery apparatus according to claim 5, wherein:a temperature sensor is disposed within or near said outlet flow passageextending from said metering pump to said mixing chamber.
 18. A liquidaeration delivery apparatus according to claim 6, wherein: a temperaturesensor is disposed within or near said outlet flow passage extendingfrom said metering pump to said mixing chamber.
 19. A liquid aerationdelivery apparatus according to claim 7, wherein: a temperature sensoris disposed within or near said outlet flow passage extending from saidmetering pump to said mixing chamber.
 20. A liquid aeration deliveryapparatus according to claim 8, wherein: a temperature sensor isdisposed within or near said outlet flow passage extending from saidmetering pump to said mixing chamber.
 21. A liquid aeration deliveryapparatus according to claim 17, further comprising a means forgenerating heat by applying a DC current to said electromagnetic coil ifsaid temperature sensor detects a temperature level equal to or lowerthan a predetermined level in a non-operating state thereof and turningon/off the applied current based upon the output from said temperaturesensor.
 22. A liquid aeration delivery apparatus according to claim 18,further comprising a means for generating heat by applying a DC currentto said electromagnetic coil if said temperature sensor detects atemperature level equal to or lower than a predetermined level in anon-operating state thereof and turning on/off the applied current basedupon the output from said temperature sensor.
 23. A liquid aerationdelivery apparatus according to claim 19, further comprising a means forgenerating heat by applying a DC current to said electromagnetic coil ifsaid temperature sensor detects a temperature level equal to or lowerthan a predetermined level in a non-operating state thereof and turningon/off the applied current based upon the output from said temperaturesensor.
 24. A liquid aeration delivery apparatus according to claim 20,further comprising a means for generating heat by applying a DC currentto said electromagnetic coil if said temperature sensor detects atemperature level equal to or lower than a predetermined level in anon-operating state thereof and turning on/off the applied current basedupon the output from said temperature sensor.
 25. A liquid aerationdelivery apparatus according to claim 17, further comprising a means forpreventing an inner pressure from rising to an excessively high levelwhich makes said electromagnetic valve open if said pressure sensordetects that the pressure in said metering pump and in said outlet flowpassage has risen to a level equal to or higher than a predeterminedlevel in an non-operating state thereof.
 26. A liquid aeration deliveryapparatus according to claim 18, further comprising a means forpreventing an inner pressure from rising to an excessively high levelwhich makes said electromagnetic valve open if said pressure sensordetects that the pressure in said metering pump and in said outlet flowpassage has risen to a level equal to or higher than a predeterminedlevel in an non-operating state thereof.
 27. A liquid aeration deliveryapparatus according to claim 19, further comprising a means forpreventing an inner pressure from rising to an excessively high levelwhich makes said electromagnetic valve open if said pressure sensordetects that the pressure in said metering pump and in said outlet flowpassage has risen to a level equal to or higher than a predeterminedlevel in an non-operating state thereof.
 28. A liquid aeration deliveryapparatus according to claim 20, further comprising a means forpreventing an inner pressure from rising to an excessively high levelwhich makes said electromagnetic valve open if said pressure sensordetects that the pressure in said metering pump and in said outlet flowpassage has risen to a level equal to or higher than a predeterminedlevel in an non-operating state thereof.
 29. A liquid aeration deliveryapparatus according to claim 21, further comprising a means forpreventing an inner pressure from rising to an excessively high levelwhich makes said electromagnetic valve open if said pressure sensordetects that the pressure in said metering pump and in said outlet flowpassage has risen to a level equal to or higher than a predeterminedlevel in an non-operating state thereof.
 30. A liquid aeration deliveryapparatus according to claim 22, further comprising a means forpreventing an inner pressure from rising to an excessively high levelwhich makes said electromagnetic valve open if said pressure sensordetects that the pressure in said metering pump and in said outlet flowpassage has risen to a level equal to or higher than a predeterminedlevel in an non-operating state thereof.
 31. A liquid aeration deliveryapparatus according to claim 23, further comprising a means forpreventing an inner pressure from rising to an excessively high levelwhich makes said electromagnetic valve open if said pressure sensordetects that the pressure in said metering pump and in said outlet flowpassage has risen to a level equal to or higher than a predeterminedlevel in an non-operating state thereof.
 32. A liquid aeration deliveryapparatus according to claim 24, further comprising a means forpreventing an inner pressure from rising to an excessively high levelwhich makes said electromagnetic valve open if said pressure sensordetects that the pressure in said metering pump and in said outlet flowpassage has risen to a level equal to or higher than a predeterminedlevel in an non-operating state thereof.